AbstractBackground: Carbapenemase-resistant Enterobacteriaceae is a major threat to public health. These microorganisms are resistant to all types of beta-lactam antibiotics.Methods: This cross-sectional study was conducted on 51 Enterobacteriaceae isolates from clinical samples in Sina Hospital and Tehran Heart Center in Iran from 2016 to 2018. Antibiotic susceptibility test was performed by disk diffusion method. Carbapenem-resistant isolates were identified by the Modified Hodge Test (MHT) and Polymerase Chain Reaction (PCR) for surveying the presence of VIM, NDM, IMMP, and OXA-48 genes.Results: Out of 51 clinical samples, 38 isolates were positive for both MHT and PCR tests, and 5 isolates were negative in both tests. The results of both tests are similar in 84.3% of the isolates.Conclusion: The MHT is an appropriate and easy method for approving carbapenemase production. Also, a laboratory can detect the carbapenemase production by identification of the KPC genes.

Background and Objectives: Methicillin-resistant Staphylococcus aureus (MRSA) is a major cause of nosocomial and community acquired infections. Detection of MRSA in laboratories is very important for treatment and appropriate infection control. The aim of this study was to evaluate cefoxitin disk diffusion method for detection of MRSA and comparison of this method with other conventional methods. Methods: A total of 175 clinical isolates of S. aureus isolated from clinical specimens were studied. The isolates were identified by conventional laboratory methods. In this respect, E-test MIC, cefoxitin and oxacillin disk diffusion methods, and MAST ID Methicillin strips were used for detection of MRSA. All disk diffusion methods were performed as recommended by NCCL and manufacturers’ guidelines. Results: Using E-test MIC, 53 out of 175 strains of S. aureus were resistant to methicillin. In addition, disk diffusion method using oxacillin disk showed that 52 strains are resistant to methicillin. In this respect, 8 strains had intermediate resistance to methicillin. For cefoxitin disk diffusion method, 52 strains were resistant to methicillin. This method had a good correlation with E-test MIC method. Meanwhile, MAST ID methicillin strips detected 47 strains that were resistant to mehicillin. Sensitivity and specificity for both cefoxitin and oxacillin disk diffusion methods were 98%and 100% respectively. However cefoxitin was better than oxacillin for detecting intermediate resistant strains of S. aureus. Sensitivity and specificity for MAST ID methicillin strips were 91% and 100% respectively. Conclusion: This study revealed that cefoxitin disk diffusion method is a good alternative for oxacillin disk diffusion method for detection of MRSA. This method is more reliable for identification of intermediate resistant strains of S. aureus.

Background: ventilator- associated pneumonia (VAP) continues to complicate the course of 8-28% patients receiving mechanical ventilation. The mortality rate for VAP is high, ranges from 24-50% and can reach 76% in some specific settings or when lung infection is caused by high risk pathogens. The etiologic agents widely differ according to the population of patients in an intensive care unit, duration of hospital stay, and prior antimicrobial therapy. Because appropriate antimicrobial treatment of patients with VAP significantly improves outcome, more rapid identification of infected patients and selection of antimicrobial agents represent important clinical goals. Our goal was determination of the VAP incidence, identification of common pathogenic causes and determination of antimicrobial resistance pattern by disk-diffusion and E.Test methods.Materials and methods: In an observational study we evaluated the microbiology and antimicrobial resistance pattern of VAP in medical Intensive Care Units (ICUs) of 2 teaching hospitals from January 2005 to January 2006. Diagnostic criteria for VAP were the radiographic appearance of a new or progressive and persistent pulmonary infiltrate in conjunction with at least 2 of the following criteria: purulent respiratory secretions, temperature > 38.5°c or < 35°c, leukocyte count >10,000 mm3 or < 1,500/mm3. Mini–BAL was planned for all of suspicious cases. For each causative pathogen, antibiotic susceptibility was determined by disk-diffusion and E.Test methods.Results: Among 114 patients under mechanical ventilation, 6 patients (5.3%) had a VAP episode, 3 patients in each hospital. In VAP patients the mean days of hospitalization were 26.3 days (± 20.92) and ICU stay were 22.8 days (± 21.53). There was a significant statistical correlation between use of H2 blockers and VAP (P< 0.05). Pseudomonas aeruginosa and Klebsiella pneumonia were isolated by mini-BAL (>104cfu/ml) in 6 patients (each pathogen in 3 cases). Antimicrobial susceptibility pattern were determined by disk-diffusion and E.Test methods and all of pathogens except one (pseudomonas aeruginosa) were resistant to ceftriaxone and ceftazidime.Conclusion: This study showed the increasing incidence of resistance to third and fourth generations of cephalosporins among gram negative bacilli that has occurred in parallel with increasing use of these drugs in our ICUs. More judiciouse use of antibiotics will be necessary to limit this trend.